The present invention relates to a frequency divider making use of Josephson junction circuits, and more particularly to a frequency divider having an operation frequency range extending even to a hundred GHz.
The upper limit of the frequencies at which frequency-division can be preformed in a frequency divider that is available in direct measurement of a frequency, microwave communication, etc. is restricted by the switching time of switching elements used in the frequency divider. Heretofore, semiconductor integrated circuit frequency dividers have been developed on a Si or GaAs substrate in which Si devices or GaAs devices are used for the switching element. However, because of a limit of the switching speed of semiconductor devices forming these frequency dividers, it was difficult to realize a frequency divider operable at 1 GHz or higher in a Si integrated circuit and a frequency divider operable at 4 GHz or higher in a GaAs integrated circuit. Accordingly it is not possible to apply the aforementioned semiconductor integrated circuit frequency divider to direct measurement of a frequency or microwave communication and the like in a high frequency band such as a 10 GHz or 20 GHz band.
On the other hand, it has been reported that a Josephson junction device that operates at a very low temperature has a switching time of about 10 ps. Therefore, there is a possibility that a frequency divider operable up to a frequency of a hundred GHz can be made by a circuit employing such Josephson junction devices. However, a frequency divider employing such Josephson junction devices has not been proposed up to now.
If a frequency divider making use of the Josephson junction circuits is realized, it may be applied, as another field of application, to frequency-division of a clock frequency in an electronic computer. In an electronic computer making use of the Josephson junction integrated circuits, it is necessary to immerse all the Josephson junction circuits having a logic function, a memory function, a control function, etc. in liquid He, because the Josephson junction integrated circuit can operate only at a very low temperature in the proximity of the liquid He temperature. Accordingly, external timing pulses necessitated for accurately and efficiency actuating a logic circuit, a memory circuit, etc. which operate at various different speeds and at different timings also, should be preferably generated by means of Josephson junction circuits. To that end, it is necessary that a pulse generator for generating a pulse train having the same repetition frequency (fundamental frequency) as a signal fed from an oscillator held under a room temperature and a frequency divider for producing a timing pulse train having a frequency of 1/2, 1/4 etc. of the fundamental frequency are realized by making use of Josephson junction circuits.